imx: imx8mp_evk: fix boot issue

The u-boot-spl.bin pad with ddr firmware conflicts with the
CONFIG_MALLOC_F_ADDR area, the ddr firmware will be overwritten
by malloc in SPL stage and cause ddr initialization not able
to finish. So update the related addresses to fix the issue.

Reported-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>